Such navigation devices are installed in transportation devices such as motor vehicles, ships, and airplanes in order to navigate the driver of the transportation device from a current location to a desired destination. The navigation devices determine the current position of the transportation device, for example, using GPS (global positioning system), and calculate a recommended route using geographic data that are stored on a storage medium.
Such a navigation device is described in German Patent Application No. DE 101 46 785, which uses a storage medium on which geographic data are stored together as map units that respectively correspond to a geographic partial region, the geographic partial regions not overlapping. In this context, the geographic data relate to either a point, which is determined through its coordinates, or to lines or surfaces that are determined by their edge points and split at map unit boundaries. To calculate a recommended route, required map units are selected and completely read by the navigation device.
A disadvantage is that the individual map units also contain a lot of detailed information relating to geography, which is not always necessary for navigation. For this reason, the scope of the geographic data that must be read, stored, and processed by the navigation device is unnecessarily broad.